Research is currently in progress on factors affecting sexual maturation in female house mice; the project is proceeding in three phases. First, various experimental sequences are being conducted to ascertain the effects of urine from various donor mice on puberty in young females. Donor types include males and females at different densities and of different ages, pregnant and lactating females and females at various stages of the estrous cycle. Male urine and urine from pregnant or lactating females accelerates puberty, whereas urine from females housed two or more per cage delays puberty. Second, six generations of artificial selection have been used to develop two sublines of mice; mice from one subline attain puberty significantly earlier than control females, whereas mice from the other subline reach puberty signficantly later than control stock females. For the four sublines which have been developed estimates of the degree of genetic determination of age of puberty are all relatively high, particularly for a reproductive trait. Third, experiments are being conducted to probe the possible mechanism of production of a maturation-delaying pheromone in the urine of grouped female mice. Ovariectomizing females does not influence pheromone production or secretion, but removing the adrenal glands leads to an absence of the pheromone in either excreted or bladder urine.